Vibrating reed controlled oscillator



April 3, 1951 M. R. WINKLER 2,547,027

VIBRATING REED CONTROLLED OSCILLATOR Filed Jan. 2, 1948 Patented Apr. 3,1951 VIBRATING REED CONTRGLLED OSCILLATOR Marion R. Winlrler, La GrangePark, Ill., assignor to Motorola, Inc., Chicago, 111., a corporation ofIllinois Application January 2, 1948, Serial No. 343

'7 Claims.

This invention relates generally to oscillators and more particularly toan oscillator system including vibrating reeds for determining thefrequency thereof so that the oscillator frequency will be held withinvery narrow limits.

Oscillator systems for producing audible tones are used in manyapplications as, for example, electronic musical instruments and inselective signalling systems. Although in some applica tions thefrequency requirements are not so severe, in certain applications it isrequired that the frequency of the oscillators be held within very smalllimits. This is the case in selective calling systems for use in mobilecommunication equipment wherein it is desired to provide a large numberof possible calls Within a limited frequency range. In order toaccomplish this satisfactorily, the tone oscillator used must be veryaccurate so that closely adjacent frequencies can be'used withoutinterference with each other. Although various means have been providedfor stabilizing oscillators, such as the use of crystals, these systemshave not been practical for low frequency operation. Further, suchsystems have been relatively complicated and expensive and, as'aplurality of oscillators are required in a selective calling systemhaving a plurality of stations, the complete system becomes relativelycomplicated and involved.

It is, therefore, an object of the present invention to provide animproved tone oscillator, the

frequency of which can be very accurately controlled.

A further object of this invention is to provide a simple toneoscillator, the frequency of which is controlled by a vibrating reedstructure.

A feature of this invention is the provision of 'a tone oscillator inwhich feedback is provided through a vibrating reed filter so thatoscillations are produced only at the natural freque cy of the reedsystem.

A further feature of this invention is the provision of an'oscillatorhaving output and input circuits individually coupled to a pair of reedssupported on a common mounting, so that feedback is provided for theoscillator at a particular frequency which depends upon thecharacteristics of the reeds.

Another feature of this inventionis the provision of a tone oscillatorwhich includes 2. vi brating reed structure for providing feedback and aphase shifting network for compensating for the phase shift produced bythe reed structure.

A still further feature of this invention is the provision of a uniquedouble reed system which is small and compact and which is adapted totransfer energy from one circuit to another circuit at one particularfrequency.

Further objects, features and advantages will be apparent from aconsideration of the follow" ing description taken in connection withthe accompanying drawings in which:

Fig. 1 is an elevation view of a plug-in double reed filter inaccordance with the invention;

Fig. 2 is an end view along the lines 2-4 of Fig. 1;

Fig. 3 is a cross-sectional view along the lines 3-3 of Fig. 2;

Fig. 4 is an enlarged detail of a pole piece of the reed structure;

Fig. 5 is an enlarged detail of the mounting bracket for the vibratingreeds;

Fig. 6 is a circuit diagram illustrating the use of the vibrating reedfilter in an oscillator circuit; and

Fig. 7 illustrates the manner in which longer reeds can be used in thevibrating reed structure.

In practicing the invention there is provided a vacuum tube oscillatorhaving input and output circuits which are coupled through a vibratingreed filter. The filter is arranged to provide the feedback necessary toproduce oscillations at a particular frequency. This is accomplished bya reed structure including a pair of reeds mounted on a common supportwith a coil about one of the reeds connected in the output circuit ofthe oscillator and a coil the other reed connected in the input circuit.The support for the reeds is so arranged that energy i transferred fromone reed to the other at the natural frequency of the vibrating reeds toprovide the feedback required to produce oscillations. To compensate forthe phase shift produced in the filter, a compensating network isprovided so that the feedback voltage will be in the proper phase toprovide sustained osciila tions.

Referring now to Figs. 1 and 2, the vibrating reed structure isconstructed as a plug-in unit including a base portion it, a coverportion H, and plug-in terminals E2. The vibrating structure l3 of, theunit is completely enclosed by base and cover to provide a neatappearing unit.

The vibrating structure is supported on the base it! by four bolts Itand includes three mag nets i5, i6 and l? having pole pieces l8 thereonwhich form two separate magnetic circuits. Coils it and 2c are providedin the magnetic cir cuits being held position by the pole pieces 13. A.pair of vibrating reeds 2i and are posi tioned in the fields produced bythe magnets and coils and are supported in a rigid member The rigidmember 23 is supported by a resilient but relatively stiff bracket whichis anchored the center magnet is by bolts 2-5. The rigid support isremovably secured to the bracket by a screw indicated at as shownclearly in 2 and 3, the magnets iii, 55 and i; and the pole pieces itconnected thereto are sup ported by the bolts it and properly positionedby cylindrical spacers 2'? which surround the bolts and position themagnets and pole pieces with respect to each other.

The magnets 55 and ii are magnetized in one direction and the magnet i5is magnetized in the opposite direction so that the pole pieces are ofthe polarities indicated by the letters S and N (representing south andnorth poles) in Fig. 3. It is, therefore, seen that a balanced systemexists which normally would allow the reeds 2i and 22 to remain at restcentrally of the pole pieces. Curent applied to the coil as will tend toincrease one field and decrease the other so that the reed El will bemoved. It is well known when currents of a particular frequency areapplied to the coil, the vibrations in the reed will reinforce eachother resulting in sustained vibrations. This frequency is knownas thenatural frequency of the reed. Such sustained vibrations will betransferred through the base 23 to reed 22 which moves toward one pairof pole pieces or the other to thereby unbalance the fields and induce avoltage in the coil 26.

Fig. 4 illustrates the detailed construction of the pole pieces E8 whichinclude openings 33 for receiving the bolts id. The pole pieces alsoinclude tongues 3! which are positioned inside the coils is and '29 tobring the fields of the magnets inside the coils and to mechanicallyposition the coils and prevent disassembly thereof. The reed support 23,bracket 24, spacers 2? and bolts it are all preferably made ofnon-magnetic material so that the required magnetic fields are notshunted thereby.

5 illustrates in detail the mounting bracket for the support 23 whichcarries the reeds 2i and The bracket 24 includes openings 32 for secu.ng the same to the center magnet and an opening 33 to receive the bolt25 for securing the 3 id member 23 thereto. "ient enough to permit thetransfer of energy fr one reed to the other so that equal and oppositevibrations are produced therein. The bracket must be stiff enough tohold the reeds in the proper position in the fields. The configurationof the bracket is such that limited universal movement of the member 23is provided. ihis llows the vibrating structure to shift toautomatically compensate for inaccuracies in con' struction.

6 illustrates a tone oscillator which may utilize the vibrating reedstructure as above described. The oscillator includes a vacuum tubehaving a cathode M, a grid 42 and a plate 33. The plate as is connectedtoa plus B power supply through resistor i l and coupled through con-'denser 55 to the winding 48 positioned about the ibrating reed fl.Energy applied to the winding ii-l will produce a field which reactswith the field produced by magnets 55 and 5b to cause v bration of thereed 4?. This vibration of the will be transferred through the rigidsupt the second reed 59. Vibration of reed h} in a suitable field whichmay be produced by agnets and ill will cause sinusoidal oscilla Thebracket 2t is re- Cir tions to be induced in the coil 50 positionedthereabout. A condenser 51 is connected across the coil is to tune thecoil so that the voltage developed thereacross at the frequency of thereeds will be increased. This voltage is applied to the input of thevacuum tube through a phase correcting network such as the network madeup of resistor 52' and condenser 53.

As is well known, the vibrating reeds ll and :39 described above willhave a natural frequency of vibration which is effective in the presentsystem to cause regenerative feedback resulting in oscillations at thisparticular frequency. It has been found that the transfer of thevibrations from reed ii to reed 9 at a frequency of maximum amplitude isaccompanied by a phase shift sometimes as great as 90 degrees. Phaseshifts are also produced by the various circuit comare positioned in themagnetic field.

ponents such as condensers 45 and 5 I. This may be corrected by shiftingthe phase of the voltage from coil {iii so that the voltage appliedthrough the coupling resistor 54 to the grid 452 of the triode ill issubstantially in phase with the voltage generated within the tube.Resistor 52 and condenser 53 are provided especially for providing thedesired phase relationship within the tube 46. It is obvious that theregenerative feedback produced through the windings at the particularfrequency to which the reeds respond will cause oscillations at thatfrequency. As the voltage induced in the coil 5E3 is substantially apure sine wave the output voltage appearing at terminal 55 will be asine wave.

It is apparent that reed structures as shown in Figs. 1 to 5 can be usedin the oscillator of Fig. 6. By use of this construction, the reedstructure can be plugged into a chassis so that both electricalconnection and mechanical support is provided by terminals l2. Onlythree terminals are required for making connection to the coils as oneside of each coil may be grounded as is apparent from Fig. 6. Themounting screws [4 may be of such length to extend through the coverportion H to thereby support the cover portion in position on the baseHi.

In order to provide oscillators having various natural frequencies,reeds of different thicknesses may be used. However, for low frequenciesthis would result in very thin reeds if the length of the reeds was heldthe same. This provides a flux path through the reed of smaller crosssection to provide a higher reluctance path and consequently a smallerdriving force. This can be overcome by use of longer reeds which mayhave a larger cross section. Longer reeds are also desirable at lowfrequencies as they permit greater over-all amplitude of vibration forthe portions of the reeds which are in the magnetic fields therebyimproving the amplitude of the induced oscillations at low frequencies.

Fig. 7 shows the manner in which longer reeds may be used in thestructure described. This is accomplished by using a longer centermagnet to which is effective to support the longer reeds i3? and St in aposition so that the ends thereof In the structure illustrated, mountingbracket 24 is secured to the longer center magnet 36 and supports themounting member 23 for the reeds in the same manner as in the structuredescribed above. ihis permits the use of identical mounting brackets andreed supports regardless of the lengths of the reeds with the difierencein lengths being compensated for by using a mag- I g net of the requiredlength in the center portion of thestructure. "l

It is apparent that the tone oscillato'r'in accordance with theinvention is of relatively simple construction. The mechanical filter iseffective to limit the feedback to a very narrow range of frequencies sothat the oscillator will always operate within this range. Withoutchanging the components of the structure except the center magnet andthe reeds, vibrating reeds of different lengths can be used to providethe feedback required at difierent frequencies.

While I have described certain embodiments of my invention, it isapparent that various changes and modifications can be made thereinwithout departing from the intended scope of the invention as defined inthe appended claims.

I claim: f f

1. In an oscillator, means for producing feedback for sustainingoscillations of a predetermined frequency including in combination,first and second magnetic reeds each having a natural frequency ofvibrations substantially equal to said predetermined frequency, amagnetic structure about said reeds including a central elongated magnetand a pair of elongated magnets spaced therefrom, pole pieces secured tosaid magnets to provide a pair of opposed magnetic fields on oppositesides of each of said reeds, supporting means for said reeds including arigid mounting member for interconnecting said reeds and a resilientsupport for securing said rigid mounting member to said central magnet,first and second windings individually positioned about said reeds andsupported by said magnetic structure, and a feedback circuit includingfirst and second windings for ap lying signals to said first winding,said first winding producing a fluctuating magnetic field superimposedon said balanced magnetic field which causes vibration of said firstreed when said fluctuations occur at said predetermined frequency, saidrigid mounting member transmitting vibrations of said first reed to saidsecond reed causing said second reed to vibrate at said naturalfrequency, said second winding translating the fluctuations a the fieldabout said second reed caused by movement thereof in said balanced fieldinto electrical oscillations occurring at said predetermined frequency.

2. In an oscillator, means for producing feedback for sustainingoscillations of a predetermined frequency comprising, first and secondmagnetic reeds each having a natural frequency of vibrationssubstantially equal to said predetermined frequency, a magneticstructure about said reeds including a central elongated permanentmagnet and a pair of elongated permanent magnets spaced therefrom, polepieces secured to said magnets to provide a pair of opposed magneticfields on opposite sides of each of said reeds, supporting means forsaid reeds including a rigid mounting member for interconnecting saidreeds and a resilient support for securing said rigid mounting member tosaid central magnet which provides limited universal movement of saidmounting member, windings about said reeds supported by said magneticstructure, and a feedback circuit including said windings for applying asignal to said winding about said first reed to thereby produce afiuctuating magnetic field superimposed on said balanced magnetic fieldwhich causes vibration of said first reed said fluctuations occur atsaid predetermined frequency, said vibration of said first reed beingtransmitted through said rigid mounting member to said second reedcausing said second reed to vibrate-at said natural frequency, saidwinding about said second reed translating the fluctuations in the fieldabout said second reed caused by movement thereof in said balanced fieldinto electrical oscillations occurring at said predeterminedfrequency,said feedback circuit including means for shifting the phase of saidelectrical oscillations to provide oscillations which are substantiallyin phase with the signals of said predetermined frequency applied tosaid winding about said first reed.

3. An oscillator comprising an electron discharge valve having input andoutput electrodes. and a feedback system coupling said input and utputelectrodes for providing regenerative feedback therebetween ata'predetermined frequency, said system including in combination, firstand second windings amagnetic structure providing a pair of magneticpaths about each of said wind-- ngs and including permanent magnet meansproviding magnetic flux through said paths of each pair in oppositedirections with respect to the associated windings, first and secondmagnetic reeds of such construction that the natural frequency ofvibration thereof is the same said predetermined frequency, said reedsbeingindividually associated with saiddfirst and second windings andpositioned adjacent to said magnetic paths about each of said windingsto reduce the reluctance thereof, mounting means interconnecting saidfirst and second magnetic reeds, means coupling said first winding tosaid output electrodes of said valve so that oscillations appliedthereto provide a fluctuating field about said first winding and saidfirst reed is caused to vibrate in response to oscillations of saidpredetermined frequency, said mounting means transmitting vibrations ofsaid first reed to said second reed to cause said second reed to vibrateat said predetermined frequency, and means coupling said second windingto said input electrodes to apply the oscillations produced in saidsecond winding by vibration of said second reed to said inputelectrodes, said last mentioned means including phase shifting means forproviding oscillations to said input electrodes of such phase to causeregenerative action in said valve.

4. An electromechanical translating device for selectively passingsignals of a predetermined frequency including in combination, first andsecond windings, a magnetic structure providing a pair of magnetic pathsabout each of said windings and including means providing magnetic fluxthrough said paths of each pair in opposite directions with respect tothe associated winding, first and second magnetic reeds having a naturalfrequency of vibration substantially the same as said predeterminedfrequency, individually associated with said first and second windingsand positioned adjacent to said magnetic paths about each of saidwindings to reduce the reluctance thereof, rigid means interconnectingsaid first and second magnetic reeds, and resilient means for supportingsaid rigid means for limited movement with respect to said magneticstructure.

5. An electromechanical translating device including in combination,first and second windings, a magnetic structure providing a pair ofmagnetic paths about each of said windings and including means providingmagnetic flux through said paths of each pair in opposite directionswith respect to the associated winding, said magnetic structureincluding symmetrically positioned pole pieces forming an air gap ineach of said magnetic paths, first and secondv magnetic reedsindividually associated with said first and second windings andpositioned adjacent to said pole pieces to reduce the reluctance of saidmagnetic paths, and a member interconnecting said first and secondmagnetic reeds for transmitting vibrations therebetween.

6. An electromechanical translating device including in combination,first and second windings, a magnetic structure including a centralpermanent magnet and a pair of permanent magnets spaced on either sidethereof, a plurality of symmetrically positioned pole pieces connectedto said magnets and providing a pair of magnetic paths about each ofsaid windings with each of said paths including an air gap therein, saidmagnets being polarized to provide magnetic flux through said paths ofeach pair in opposite directions with respect to the associated winding,first and second magnetic reeds individually associated with said firstand second windings and positioned adjacent to said air gaps in saidmagnetic paths to reduce the reluctance of said paths, rigid meansinterconnecting said first and second magnetic reeds, and resilientmeans for supporting said rigid means with respect to said magneticstructure.

7. An electromechanical translating device for 3 selectively passingsignals of a predetermined frequency including in combination, first andsecond windings, a magnetic structure including a central-permanentmagnet and a pair of permanent magnets spaced on either side thereof, aplurality of symmetrically positioned pole pieces connected to saidmagnets and providing a pair of magnetic paths about each of saidwindings with each of said paths including an air gap therein, saidmagnets being polarized to provide magnetic flux through said paths ofeach pair in opposite directions with respect to the winding associatedwith each pair, first and second magnetic reeds having a naturalfrequency of vibration which is the same as said predetermined frequencyindividually associated with said first and second windings andpositioned intermediate said magnetic paths adjacent said air gapsthereof to reduce the reluctance of said paths, and meansinterconnecting said first and second magnetic reeds for transmittingvibration therebetween.

MARION R. WINKLER.

REFERENQES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,516,947 Beindorf Nov. 25, 19241,919,139 Walton July 18, 1933 2,034,787 Williams, Jr Mar. 24, 1936

